rcd tripping

[flinty]

I have a problem with the rcd tripping on the downstairs ring main.
I have taken every plug out of every socket and it still does it. It doesn't trip straight away it takes about 5 seconds before it trips. The rcd doesn't trip at all if I have the downstairs mcb in the off position.
The problem suddenly started this afternoon.

Is there any way to find where the fault is or could it be that the rcd has become over sensitive and is nuisance tripping?

 

[electronicsuk]

If the problem disappears with a particular MCB switched off and yet still occurs when there are no loads on the problem circuit, it's very unlikely that the RCD is to blame. More likely is that you have a Live-Earth fault somewhere on the circuit, but unless you're handy with a multimeter and have plenty of time on your hands, it may be better left to an electrician to fix. That is, unless you've done anything obvious just recently that could have caused the problem; knocking nails into walls, spilling water on or near electrical accessories, etc.

 

[Christhescott]

You've probably done this but switch off any switch fuses. Also is your central heating fed from this circuit? could be a knackered pump/valve.

 

[JohnD]

any sign of rodents, including under the floor?

 

[flinty]

I will let you know as soon as I have had time to check. Unfortunately whoever wired the house has got one side of the kitchen on the downstairs circuit and the other side on the upstairs one.